Abstract: :
Purpose: Myristoyl switch is a feature of several peripheralmembrane proteins. This unique molecular property is best illustratedby the ‘calcium–myristoyl switch’ of recoverin(Rv) which is a calcium–binding protein present in retinalrod cells of vertebrates. Rv contains an amino–terminalmyristoyl group (Myr) and acts as a calcium sensor by regulatingthe rod cell response to the changes in intracellular calcium.Indeed, the binding of two calcium ions to Rv induces the extrusionof its Myr which increases its affinity for membranes. However,in the calcium–free form, the Myr is sequestered in ahydrophobic cleft of Rv. Little is known about the parametersresponsible for the modulation of the membrane binding of Rv.Consequently, this study was performed to determine the involvementof the charged amino acids of Rv as well as its Myr in its membranebinding.Methods: Polarization–modulated infrared reflection absorptionspectroscopy (PM–IRRAS) combines Fourier transform mid–IRreflection spectroscopy with rapid polarization modulation ofthe incident beam. This spectroscopic method is very sensitiveto characterize thin films spread at the air/water interface.We have thus used PM–IRRAS and Surface Pressure Measurements(SPM) to measure Rv adsorption onto phospholipid monolayersat the air–water interface and to probe protein structurein presence of different ions and phospholipids.Results: PM–IRRAS spectra indicate that Rv contains amajor proportion of α–helix and that its folding is preservedat the air/water interface. SPM of the adsorption of myristoylatedand unmyristoylated Rv shows clearly that both the myristoylgroup and hydrophobic residues contribute to Rv membrane binding.Conclusions: Rv preferentially binds certain phospholipids andions other than calcium can increase its affinity for membranes.These results allow a better understanding of the parametersresponsible for the membrane binding of Rv and also for peripheralproteins in general.